Title: Star Brightness: Don’t Judge a Book by Its Cover Grade Level: 9th Grade Course: Earth Science
Lesson Overview:
In this lesson students will learn what factors determine the brightness of a star and how astronomers determine the brightness of a star through magnitudes. Students will be given a brief history of the system used by astronomers to classify the brightness of a star and then given a worksheet to test their knowledge of understanding the numerical values of magnitudes. Students will also learn the difference between apparent and absolute magnitude of a star through a demonstration using flashlights as stars of varying luminosities. Through this demonstration students will learn how the intrinsic brightness of a star and its distance from Earth both contribute to a star’s brightness. Students will also be corrected of the misconception that what they see as a faint star at night may be in actuality the star with the greatest magnitude and luminosity but its distance from Earth tricks are eyes into thinking it’s a faint star.
Learning Performances:
From this lesson students will be able to:
Explain how astronomers rate the brightness of a star
Determine if a star is bright or faint based on the numerical magnitude of the star
Rank stars from brightest to faintest based on their numerical magnitudes
Distinguish between absolute and apparent magnitude
Identify and the factors that contribute to a stars brightness
Explain how a star’s magnitude can depend on both intrinsic brightness and distance from Earth
Time Required: (Two 50min Periods) Day 1 – Rating the brightness of a star
10-min List and discuss star observations ( From Star Observation 1 homework)
5-min Brainstorming: What makes a star bright? Why?
15-min How to categorize a star’s brightness or magnitude? Past and present systems of categorizing star magnitudes
7min – Student Activity: Brightest Objects in Our Sky Worksheet
8- min Review and discuss answers
5-min Explain homework (Star Observation 2)
Day 2 - Factors that affect a star’s magnitude
10-min Review previous night observation to Orion star magnitude ranking, post answer key and discuss answer
5-min Brainstorming: Why are some stars brighter than others? List potential factors
20-min Flashlight demonstration and discussing the terms absolute and apparent magnitude
15-min Student Activity: Which star is brighter? Sun and Betelgeuse comparison, apparent vs. absolute magnitude worksheet
Instructional Sequence for Day 1
Introducing the lesson:
To activate students’ prior knowledge about stars I assigned the class a star gazing homework activity where students were suppose to go outside for 15- 20 minutes look up at the stars in the sky and write down 10 things that they observed. To begin the class I will ask students what observations they made during their star gazing assignment from the previous night. What did they see? Were they able to see any stars? If so, what did they look like? Did they see any constellations? If so, which ones? I will go around the room asking each student to give me one observation that they made. I will write each observation on the board. Once everyone has contributed we will discuss the observations they made. To also activate prior knowledge I will ask students why they think they observed some of the things they saw. As we go through each observation I will survey the class to see how many other students made the same observation. I will guide the discussion towards what students observed about the stars specifically. If the observation wasn’t listed, I’ll ask them if they noticed if some stars appeared brighter than others. If the observation was listed, I’ll ask students why they think some stars look brighter than others. I will write the class responses on the board. After I will tell the students that the brightness of a star is called the star’s magnitude. By measuring star magnitudes one can determine which star is brighter.
Instructional Activities:
After the opening discussion I will give students a brief lecture on the system astronomers use to categorize stars based on their magnitude. I will explain to them that the first system was developed about 2,000 years ago by the Greek astronomer Hipparchus. In his simple method the brightest stars were labeled first magnitude while the faintest stars visible to the eye were sixth magnitude. The remaining stars fell somewhere in between. In the Hipparchus system, the larger the magnitude number, the fainter the star. Then I will talk about the modern system that astronomers use today that is similar to Hipparchus’s. Today the brightest objects have a negative magnitude values. Also with the use of modern telescopes that are more powerful, star magnitudes can be categorized up to ninth and tenth magnitudes. But these stars cannot be observed by the naked eye, only with telescopes. Lastly, I will explain hat a one magnitude jump ( say from first to second or second to third) corresponds to a change in brightness of 2.5 times. Therefore, a first magnitude star is 6.3 times brighter than a third magnitude star (2.5 x 2.5 = 6.3). This mini lecture will give students a brief history about how ancient astronomers used to observe stars and show them how some of those old methods are still used today. This lecture also sets the introduction to stars. It’s important that students know how to tell if a star is bright or faint because it will play a larger role when it comes to classifying and determining the age of a star, which they will learn about later in the unit.
After the lecture, I will pass out a worksheet to the class that has the names of the brightest objects found in our sky listed along with their numerical magnitudes. Students will be given about 7 minutes to look over the magnitudes and based on what they have just learned about rank the magnitudes from brightest to faintest. Students will have the option of working individually or with a partner to complete the worksheet.
Concluding the Lesson:
When students have completed the worksheet we will go over the answers and discuss them together as a class. I will ask the students to explain why they came up with the answer that they did so that I understand the thinking process the students used to determine their answers and so I can correct any misconceptions that the students may have after learning the new material. After I feel that all of the students have a good grasp on the new material I will pass out and explain the sheet for the star gazing 2 homework assignment students are expected to complete that night (provided there is good weather).
Instructional Sequence for Day 2
Introducing the lesson:
When students walk into the classroom I will have the Orion picture that was on their homework sheet drawn on the board with the blank spots next to each star. I will start the class by asking students what they observed and how they ranked the Orion’s stars. I will list the students’ ranks for the stars next to each blank. After about six students volunteer their answers we will look at the lists as a whole class to see if everyone had the same answers or not. The class will then discuss the answers and what they observed the previous night. After, I will write the correct rank numbers in the blanks and discuss why those are the correct numbers by giving students the exact magnitude for each star.
Next I will ask the class again why do some stars appear brighter than others in the night sky? I will write down the responses on the board and have each student explain their reasoning behind their answers. The two specific answers I will be looking for are the internal brightness of a star and the star’s distance away from Earth. If these answers are not on the list I will guide the discussion to these answers. If they are listed on the board I will survey the class to see which reason they think is the actual answer. After discussing the question and the answer possibilities, I will tell the students that stars can appear brighter due to their distance from the Earth and their internal brightness.
Instructional Activities:
To show the class that the brightness can depend on EITHER of the two answers from above I will give the class a brief demonstration using two flashlights of different sizes. First I will have the entire class stand in the front of the classroom. Then I will shut the blinds and all of the lights off to make the room as dark as possible. Next I will have two student volunteers each hold a flashlight and stand next to each other facing the front of the classroom and the class at the same distance. I will then ask the class based on the two flashlights what do they see? Which star is brighter? Fainter? After I will have the student holding the “bright star” move backwards further away from the faint star and the rest of the class. While the student is walking backwards I will ask the class what do they notice about the star’s brightness? Is it getting fainter? It will appear that the brightness is becoming more like the brightness of the fainter/closer star. Next I will ask the students what would happen if the star were to increase its distance further passed the end of the wall in the classroom? Will it still be the brightest star? Why or why not? At this point I expect the students to answer that the star will not be the brightest star anymore because as they are looking at the flashlights they see that the brightest star is not as bright because it is further away making the fainter star appear the brightest. Once I get this response I will explain to the students that they are incorrect because what they are looking at is the apparent magnitude of the star as oppose to the absolute magnitude.
Once all of the lights are turned back on and students are sitting in their seats I will ask them how bright was the star Betelgeuse that they observed in the constellation Orion? Next I will ask them how bright of a star is our Sun? Which one is brighter? Why? Again I expect the students to answer that the sun is brighter because it is bigger looking in the sky and because its brightness gives us our daylight. I will explain to the class that the star Betelgeuse is thousands of times larger then are own Sun. But the reason it looks so faint is because it is 550 – light years away where our sun is only 93 million miles away. Next I will explain that the brightness of an object seen from Earth is called the apparent magnitude. It’s the way an object appears in our sky. But the absolute magnitude is the magnitude seen at a predetermined yardstick distance away (32.6 light years). This form of magnitude is what astronomers use to determine the inherent brightness of a star. Therefore, stars with distances less than 32.6 light years away from Earth will have an absolute magnitude less than their apparent. Any star greater than that distance away will have an absolute magnitude grater than it’s apparent.
Concluding the Lesson:
Students will be handed The Apparent vs. Absolute worksheet with a list of stars and their apparent and absolute magnitudes. Based on what they just learned about in class students will answer questions based on the table. Students will have the option of working individually or with a partner. They will be given the remaining class time to work on these sheets. If they are not completed they are to be finished at home and the answers will be reviewed the following day.
Assessing Student Understanding:
The students will be assessed by:
Their participation in discussions
The completion of all worksheets that follow the activities
Ability to explain their reasoning behind their answers
Ability to distinguish between apparent and absolute magnitude
Ability to explain what makes a star bright
Ability to explain how astronomers use magnitude to determine star brightness
Cautions:
The only caution needed to be taken in this lesson is to make sure that any desks or objects are cleared from the center of the room during the flashlight demonstration so that student volunteers will not trip over anything in the dark.
Sources:
Harrington, P, & Pascuzzi, E (1994). Astronomy For All Ages: Discovering the Universe Through Activities For Children And Adults.Old Saybrook: The Globe Pequot Press.
Title: Star Brightness: Don’t Judge a Book by Its Cover
Grade Level: 9th Grade
Course: Earth Science
Lesson Overview:
In this lesson students will learn what factors determine the brightness of a star and how astronomers determine the brightness of a star through magnitudes. Students will be given a brief history of the system used by astronomers to classify the brightness of a star and then given a worksheet to test their knowledge of understanding the numerical values of magnitudes. Students will also learn the difference between apparent and absolute magnitude of a star through a demonstration using flashlights as stars of varying luminosities. Through this demonstration students will learn how the intrinsic brightness of a star and its distance from Earth both contribute to a star’s brightness. Students will also be corrected of the misconception that what they see as a faint star at night may be in actuality the star with the greatest magnitude and luminosity but its distance from Earth tricks are eyes into thinking it’s a faint star.
Learning Performances:
From this lesson students will be able to:
Links to Standards or Benchmarks:
Learning Goal 2
Materials Needed:
Time Required: (Two 50min Periods)
Day 1 – Rating the brightness of a star
Day 2 - Factors that affect a star’s magnitude
Instructional Sequence for Day 1
Introducing the lesson:
To activate students’ prior knowledge about stars I assigned the class a star gazing homework activity where students were suppose to go outside for 15- 20 minutes look up at the stars in the sky and write down 10 things that they observed. To begin the class I will ask students what observations they made during their star gazing assignment from the previous night. What did they see? Were they able to see any stars? If so, what did they look like? Did they see any constellations? If so, which ones? I will go around the room asking each student to give me one observation that they made. I will write each observation on the board. Once everyone has contributed we will discuss the observations they made. To also activate prior knowledge I will ask students why they think they observed some of the things they saw. As we go through each observation I will survey the class to see how many other students made the same observation. I will guide the discussion towards what students observed about the stars specifically. If the observation wasn’t listed, I’ll ask them if they noticed if some stars appeared brighter than others. If the observation was listed, I’ll ask students why they think some stars look brighter than others. I will write the class responses on the board. After I will tell the students that the brightness of a star is called the star’s magnitude. By measuring star magnitudes one can determine which star is brighter.
Instructional Activities:
After the opening discussion I will give students a brief lecture on the system astronomers use to categorize stars based on their magnitude. I will explain to them that the first system was developed about 2,000 years ago by the Greek astronomer Hipparchus. In his simple method the brightest stars were labeled first magnitude while the faintest stars visible to the eye were sixth magnitude. The remaining stars fell somewhere in between. In the Hipparchus system, the larger the magnitude number, the fainter the star. Then I will talk about the modern system that astronomers use today that is similar to Hipparchus’s. Today the brightest objects have a negative magnitude values. Also with the use of modern telescopes that are more powerful, star magnitudes can be categorized up to ninth and tenth magnitudes. But these stars cannot be observed by the naked eye, only with telescopes. Lastly, I will explain hat a one magnitude jump ( say from first to second or second to third) corresponds to a change in brightness of 2.5 times. Therefore, a first magnitude star is 6.3 times brighter than a third magnitude star (2.5 x 2.5 = 6.3). This mini lecture will give students a brief history about how ancient astronomers used to observe stars and show them how some of those old methods are still used today. This lecture also sets the introduction to stars. It’s important that students know how to tell if a star is bright or faint because it will play a larger role when it comes to classifying and determining the age of a star, which they will learn about later in the unit.
After the lecture, I will pass out a worksheet to the class that has the names of the brightest objects found in our sky listed along with their numerical magnitudes. Students will be given about 7 minutes to look over the magnitudes and based on what they have just learned about rank the magnitudes from brightest to faintest. Students will have the option of working individually or with a partner to complete the worksheet.
Concluding the Lesson:
When students have completed the worksheet we will go over the answers and discuss them together as a class. I will ask the students to explain why they came up with the answer that they did so that I understand the thinking process the students used to determine their answers and so I can correct any misconceptions that the students may have after learning the new material. After I feel that all of the students have a good grasp on the new material I will pass out and explain the sheet for the star gazing 2 homework assignment students are expected to complete that night (provided there is good weather).
Instructional Sequence for Day 2
Introducing the lesson:
When students walk into the classroom I will have the Orion picture that was on their homework sheet drawn on the board with the blank spots next to each star. I will start the class by asking students what they observed and how they ranked the Orion’s stars. I will list the students’ ranks for the stars next to each blank. After about six students volunteer their answers we will look at the lists as a whole class to see if everyone had the same answers or not. The class will then discuss the answers and what they observed the previous night. After, I will write the correct rank numbers in the blanks and discuss why those are the correct numbers by giving students the exact magnitude for each star.
Next I will ask the class again why do some stars appear brighter than others in the night sky? I will write down the responses on the board and have each student explain their reasoning behind their answers. The two specific answers I will be looking for are the internal brightness of a star and the star’s distance away from Earth. If these answers are not on the list I will guide the discussion to these answers. If they are listed on the board I will survey the class to see which reason they think is the actual answer. After discussing the question and the answer possibilities, I will tell the students that stars can appear brighter due to their distance from the Earth and their internal brightness.
Instructional Activities:
To show the class that the brightness can depend on EITHER of the two answers from above I will give the class a brief demonstration using two flashlights of different sizes. First I will have the entire class stand in the front of the classroom. Then I will shut the blinds and all of the lights off to make the room as dark as possible. Next I will have two student volunteers each hold a flashlight and stand next to each other facing the front of the classroom and the class at the same distance. I will then ask the class based on the two flashlights what do they see? Which star is brighter? Fainter? After I will have the student holding the “bright star” move backwards further away from the faint star and the rest of the class. While the student is walking backwards I will ask the class what do they notice about the star’s brightness? Is it getting fainter? It will appear that the brightness is becoming more like the brightness of the fainter/closer star. Next I will ask the students what would happen if the star were to increase its distance further passed the end of the wall in the classroom? Will it still be the brightest star? Why or why not? At this point I expect the students to answer that the star will not be the brightest star anymore because as they are looking at the flashlights they see that the brightest star is not as bright because it is further away making the fainter star appear the brightest. Once I get this response I will explain to the students that they are incorrect because what they are looking at is the apparent magnitude of the star as oppose to the absolute magnitude.
Once all of the lights are turned back on and students are sitting in their seats I will ask them how bright was the star Betelgeuse that they observed in the constellation Orion? Next I will ask them how bright of a star is our Sun? Which one is brighter? Why? Again I expect the students to answer that the sun is brighter because it is bigger looking in the sky and because its brightness gives us our daylight. I will explain to the class that the star Betelgeuse is thousands of times larger then are own Sun. But the reason it looks so faint is because it is 550 – light years away where our sun is only 93 million miles away. Next I will explain that the brightness of an object seen from Earth is called the apparent magnitude. It’s the way an object appears in our sky. But the absolute magnitude is the magnitude seen at a predetermined yardstick distance away (32.6 light years). This form of magnitude is what astronomers use to determine the inherent brightness of a star. Therefore, stars with distances less than 32.6 light years away from Earth will have an absolute magnitude less than their apparent. Any star greater than that distance away will have an absolute magnitude grater than it’s apparent.
Concluding the Lesson:
Students will be handed The Apparent vs. Absolute worksheet with a list of stars and their apparent and absolute magnitudes. Based on what they just learned about in class students will answer questions based on the table. Students will have the option of working individually or with a partner. They will be given the remaining class time to work on these sheets. If they are not completed they are to be finished at home and the answers will be reviewed the following day.
Assessing Student Understanding:
The students will be assessed by:
Cautions:
The only caution needed to be taken in this lesson is to make sure that any desks or objects are cleared from the center of the room during the flashlight demonstration so that student volunteers will not trip over anything in the dark.
Sources:
Harrington, P, & Pascuzzi, E (1994). Astronomy For All Ages: Discovering the Universe Through Activities For Children And Adults.Old Saybrook: The Globe Pequot Press.
Teaching Resources: